Licensed mobile access (LMA) communication systems provide mobile wireless communications over large areas to individuals using wireless handsets. Licensed wireless systems include cellular telephone systems and/or Personal Communication Services (PCS) telephone systems. Wireless handsets include cellular telephones, PCS telephones, wireless-enabled personal digital assistants, wireless modems, and the like.
Licensed mobile access communication systems utilize public wireless signal frequencies that are licensed from a government entity. Licensees pay large fees for access to these frequencies, and make large capital investments in base station and switching equipment which is required to support communications over extended geographical areas. As a result, the cost of licensed wireless communication service is generally higher than voice and data services over wired communication networks such as the public switched telephone network (PSTN) and private cable systems, which do not pay license fees and which have lower and/or fully amortized capital costs.
Typically, licensed wireless base stations are installed approximately a mile apart from one another and mobile subscribers are handed off from one base station to another as the subscribers move through the coverage areas (cells) of each base station. The quality of the link between the wireless transceiver and any base station is dependent on factors such as weather conditions, distance between the base station and the subscriber, and multipath interference. In contrast, the quality of wired communication services is not affected by any of the aforementioned factors. As a result, the quality and reliability of service (e.g., voice quality, speed of data transfer and bit-error rate) in licensed wireless systems is generally inferior to the quality of service afforded by wired connections. Furthermore, in many areas, the availability of wired communication services is greater than the availability of licensed wireless communication services. Thus, the user of licensed wireless communication systems pays relatively high fees for limited availability and relatively low quality service.
As noted above, wired connections are extensively deployed and generally perform at a lower cost with higher quality voice and higher speed data services. The problem with wired connections is that they constrain the mobility of a user. To bridge the gap, unlicensed mobile access (UMA) technology has been developed to enable dual-mode (LMA and UMA) wireless handsets to access voice and data services provided by core mobile network through unlicensed wireless access points, such as IEEE 802.11 (e.g., Wi-Fi) access points or Bluetooth access points, for example. This technology is designed to seamlessly handover a licensed wireless connection to an unlicensed wireless connection whenever an unlicensed wireless link to a wired network is available. The unlicensed wireless connections operate over limited ranges (e.g., up to 100 meters) and provide high quality and high reliability links to wired Internet Protocol (IP) access networks.
UMA technology is described in detail in commonly owned copending U.S. Pat. No. 7,640,008, entitled “Apparatus And Method For Extending The Coverage Area Of A Licensed Wireless Communication System Using An Unlicensed Wireless Communication System,” filed Dec. 15, 2004 and incorporated herein by reference. In addition, a standard specification for UMA technology has been adopted by the European Telecommunications Standards Institute (see, ETSI TS 143 318 v6.0.0 2005-01) with respect to GSM and GPRS communication services.
A dual-mode wireless handset is capable of switching automatically and seamlessly between licensed and unlicensed mobile access networks. However, dual-mode operation exacts a cost in battery power, consumed by the unlicensed radio transceiver to support scanning for unlicensed wireless access points (UWAPs) while the handset is operating in cellular voice or data mode. For example, if the unlicensed radio is turned on every 2.5 seconds for access point scanning (a typical default scanning rate), the average current drain might be 2.2 milliamperes (ma) for a typical IEEE 802.11 chipset (e.g., the Broadcom BCM4317 b chipset). The average current drain of the cellular radio in standby mode might be 2.5 ma, so the total power consumption of the dual-mode handset could be approximately twice that of a standalone cellular handset. Decreasing the default scan rate of the unlicensed radio will reduce the power consumption, but decreasing the scan rate too much will introduce delays (latency) in acquiring and accessing unlicensed wireless access points that are unacceptable to mobile subscribers. The UMA standard does not specify any mechanism for power management for the unlicensed radio subsystem in a dual-mode handset.